In the spirit of the spooky season, the two may be donning the cloak of fun and games, but as Stewart says, he has a grown-up goal: to revive the moderate center of our civic discourse.

The decision to join forces speaks volumes about their underlying motivations, says Mr. Jones, author of “Entertaining Politics: Satiric Television and Political Engagement.” “This rally is about the serious side of satire.“

What they are doing is much bigger than a single election cycle, he adds. The two comics “are involved in an entirely different enterprise than Beck's, [Sean] Hannity's, [Rachel] Maddow's, et al,” he says. While Stewart is famous for protesting that his show is nothing but “fake news,” he has also said that he represents the "disenfranchised center" or "distracted center." If mainstream journalism no longer occupies a neutral middle ground, and satirists feel like they are two of the last public figures who might remind us of Roosevelt's dictum that "the only thing we have to fear is fear itself," then, says Jones, "that says a lot about what our political culture, and the media that help shape it, have become.”

However cloaked, he adds, this is the satirist's plea for sanity in a hyperventilated moment of fear and hysteria.

Nonetheless, the event is set on the doorstep of the Nov. 2 election, which makes its potential impact with younger voters undeniable, says Ari Berman, a political correspondent for The Nation. The younger demographic, which came out so effectively for Obama in 2008, has been noticeably disaffected in this midterm election. It's possible that a major event hosted by two media figures with such caché among younger voters “could easily help to mobilize action in time for the election,” he says. One thing is certain, “all the media will be there, so it will be sure to get coverage.“

If team Colbert-Stewart stays with its strong suit, namely comedy, this could affect the election, agrees political scientist Saladin Ambar of Lehigh University in Bethlehem, Pa. The president is often at his best when he is funny, he notes in an e-mail. “As the whole Tina Fey-Sarah Palin episode demonstrated, humor can eviscerate an image or candidate as well as any 15-minute stump speech. As the Democratic base struggles with an enthusiasm gap, perhaps Stewart can at least give a good many on the left reason to get involved beyond the logical and very real possibility of Dems losing the House."

"Voting is an illogical action,” he adds, “and humor can stir the passions as much as anything.”

But this is precisely the challenge the pair faces in mounting what is arguably an event without precedent, says Syracuse University media pundit Robert Thompson. "When have we ever seen something like this?”

History shows many powerful rallies by people with clear points of view, from Martin Luther King Jr., “even Glenn Beck,” he says. But Stewart and Colbert are operating with multiple levels of communication – from the serious, underlying message that Stewart seems to desire to the joke-within-a-joke persona of Colbert’s faux conservative talk show host. It will be difficult to balance those subtleties inside a format that calls for slogan-like clarity, he says, adding that Stewart has been at his least effective in his unfunniest moments, such as his election night coverage. “Their fan base will come expecting comedy, and delivering that in this kind of setting will be the biggest challenge they face,” says Mr. Thompson.

“It’s entirely possible this could end up being the very kind of thing that both he and Colbert do so well at skewering.”